It was discovered about a year ago that an apparently damaging reaction manifested by a 50% decrease in aerobic glycolysis and glutathione (GSH) content occurs in the isolated rat retina when exposure to weak light for 1/2-3 hours is coupled with hyperthermia. A low extracellular calcium concentration prevented these effects from occurring. Based upon these preliminary results, the proposed research is designed to uncover the initiating reactions of light damage using the isolated rat retina as model of the in-vivo conditions, especially of the rhodospin-mediated damage. The specific aims are: 1) To measure the effects of light on the rate of glycolysis as a function of the intensity and duration of the light; 2) To determine the action spectrum of the light producing the decrease in glycolysis; 3) To measure the capacity for recovery from the effects of light by permitting rhodospin regeneration, adding 11-cis retinal; 4) To study the relationship between the initial long-term steady-state concentration of rhodopsin and the effectiveness of light on glycolysis; 5) To study the role of retinal accumulation, measured by high performance liquid chromatography in relation to the light-induced changes in glycolysis and GSH; 6) To measure the effects of light on glycolysis and GSH as function of the extracellular concentration of calcium, and to initiate studies to evaluate whether a change in the plasma membrane is responsible for a damaging increase in intracellular calcium concentration; 7) To relate the occurrence and magnitude of lipid peroxidation in the outer segments of light exposed retinas to the decrease in GSH and glycolysis; 8) To study glucose metabolism in order to understand the decrease of glycolysis and GSH content during light using measurements of 2-deoxyglucose uptake including autoradiographic techniques, oxygen uptake, glucose oxidation and hexose monophosphate shunt activity; and 9) To study the morphology of the isolated retina by light abd electron microscopy in order to ascertain that the effects of light manifest a pathological reaction. It is expected that these studies will provide information on the initiating reactions responsible for the rhodopsin-mediated light damage and possibly provide clues for the mechanisms of cone pigment-mediated cone cell death.